1. Field of the Invention
The present invention relates to a battery charger for charging a secondary battery.
2. Description of the Related Art
In the conventional battery charger, even when a secondary battery is in electrically non-connected condition, a voltage is output at an output terminal for charging as long as power is supplied to an input.
In most battery charger, when the secondary battery is not electrically connected, an output terminal for charging is held in exposed condition. Then, it is highly possible to cause shorting in the output terminal by metal or the like. As set forth above, even when the secondary battery is in electrically non-connected condition, the battery charger output voltage for charging. Therefore, once shorting of the output terminal is caused, abnormal heating is caused within the battery charger or thermal break down of the element in the battery charger can be caused.
On the other hand, the conventional battery charger can charge even for battery other than dedicated secondary battery. However, when the secondary battery other than dedicated secondary battery is erroneously charged, it is possibly cause lowering of performance of the secondary battery, cause damaging or leakage of the secondary battery.
The present invention has been worked out in view of the problem set forth above. It is therefore an object of the present invention to provide a battery charger which can avoid possibility of output shorting while the a secondary battery is not connected and prevent use of a secondary battery other than dedicated one.
In order to accomplish the above-mentioned and other objects, a battery charger comprises battery charging control means for supplying a charge current to a predetermined secondary battery via an output terminal, and output cut-off means for cutting off connection between the output terminal and the battery charging control means when the predetermined secondary battery is not loaded and for establishing connection between the output terminal and the battery charging control means when the predetermined secondary battery is loaded. As set forth above, the present invention is completely cut-off the output by the output cut-off means when the predetermined secondary battery is not loaded in the main body of the battery charger, and starts charging of the secondary batter by turning ON the power source line when the predetermined secondary battery is loaded.
On the other hand, as one example of construction of the battery charger according to the present invention, the output cut-off means has a contact inserted between the output terminal and the battery charging control means in series, and is constructed with a magnetic field detecting switch, such as a reed switch, which closes the contact when a magnetic field by magnetic field generating mean, such as a magnet, built in the predetermined secondary battery is detected.
On the other hand, as another example of construction of the battery charger according to the present invention, the output cut-off means has magnetic field detecting means, such as reed switch, Hall IC or the like, for detecting a magnetic field by magnetic field generating means built-in the predetermined secondary battery, and a switching element, such as field effect transistor or the like, inserted between the output terminal and the battery charging control means in series and connecting the output terminal and the battery charging control means when the magnetic field is detected by the magnetic field detecting means.
As a further example of the construction of the battery charger according to the present invention, the output cut-off means comprises a mechanical switch inserted between the output terminal and the battery charging control means in series and closing the contact in response to operation of a predetermined member provided in the predetermined secondary battery.
As a still further example of the construction of the battery charger according to the present invention, the predetermined member provided on the predetermined secondary battery is a projecting portion, and a recess to engage with the projecting portion is formed in a main body of the battery charger, and the mechanical switch is provided on a bottom of the recessed portion.
On the other hand, a yet further example of the construction of the battery charger according to the present invention, the output cut-off means comprises a mechanical switch opened and closed depending upon operation by a predetermined member arranged in the predetermined secondary battery, and a switching element inserted between the output terminal and the battery charging control means in series and establishing connection between the output terminal and the battery charging control means when the mechanical switch is placed in a condition indicative of loading of the predetermined secondary battery.